Activity of neurons in the bed nucleus of the stria terminalis (BNST) plays a central role in the normal adaptive response to stress. However, chronic release of stress hormones into the BNST also plays a critical role in several central and peripheral pathologies, including anxiety disorders, posttraumatic stress disorder (PTSD), stress-induced drug abuse, cardiovascular disease, as well as gastrointestinal disorders. To date the cellular mechanisms underlying the switch from a normal adaptive response to a psychopathological state remain unknown. The long-term objectives of this proposal are to delineate the cellular mechanisms contributing to the pathological switch in BNST function, with the hope of identifying novel targets for clinical intervention. The selective serotonin (5-HT) reuptake inhibitors (SSRIs) are the first line drugs of choice in treating many stress-related disorders suggesting that abnormal 5-HT function in key areas, such as the BNST may play an important role in the development of these disorders. We have shown that 5-HT inhibits the majority of BNST neurons in vitro, and evokes an anxiolytic response in vivo. Moreover, acute release of the stress hormone corticotrophin releasing factor (CRF) facilitates the inhibitory response of BNST neurons to 5-HT, suggesting that an interaction between these two systems contributes to the normal adaptive response to stress. Our data suggest that repeated restraint stress (RRS) results in a long lasting enhancement of anxiety-like behavior that is associated with a significant reduction in the mRNA expression of inhibitory 5-HT1A receptor subunits, and an increase in excitatory 5-HT2C/7 receptor subunits in BNST neurons. These data suggest that RRS switches the 5-HT response of BNST neurons from inhibition to excitation. In addition, RRS selectively attenuates the expression of mRNA for the Kv4.2 subunit of the inhibitory transient outward potassium current (IA). Significantly, pilot data suggests that the response to RRS can be blocked by prior administration of a CRF1 receptor antagonist, or a histone-deacetylase inhibitor, which alters gene transcription. Our hypothesis is that in RRS, repeated CRF1 receptor activation initiates a cascade of events that disrupts transcriptional regulation of gene expression resulting in an increase in the excitability of BNST neurons, and particularly CRF-containing neurons, and shifting their response to 5-HT in favor of excitation. We propose that similar shifts in BNST excitability may contribute to the etiology of anxiety disorders and PTSD. Here, we will use patch clamp electrophysiology, molecular biology, and behavioral studies in rats and in a novel transgenic mouse in which a green fluorescent protein (GFP) is expressed in CRF-neurons to test our hypotheses. Two specific aims are proposed. Specific Aim #1 will characterize the effects of repeated restraint stress on gene expression and physiological properties of neurons in the anterolateral BNST of the rat. Specific Aim #2 will characterize the effects of repeated restraint stress on gene expression and physiological properties of CRF-containing neurons of the mouse anterolateral BNST.